Molybdenum (Mo), an essential microelement for plants, animals, and microorganisms, is reported can reduce soil nitrogen (N) residues and regulate plant root growth, but little is known about its effect on soil N transformation in plant-root region. A specially designed rhizobox was used in the present study to investigate the N processes in rhizosphere and non-rhizosphere soils of winter wheat applied with different rates of Mo fertilizer. (1) In the rhizosphere soil, pH values increased with increasing rates of Mo application, nitrate (NO3--N) accumulated at the rates of 0.15 and 0.3 mg Mo kg-1, potential denitrification activity (PDA) was significantly reduced by application of 0.15-1 mg Mo kg-1, and the copy numbers of narG and nosZ genes were increased by application of 0.15-1 mg Mo kg-1. (2) In the non-rhizosphere soil, NO3--N content decreased by application of 0.15-0.3 mg Mo kg-1, and narG gene abundance increased obviously by application of 0.3-1 mg Mo kg-1. (3) Soil pH, NO3--N, apparent nitrification rate (ANR), and nosZ gene abundance were significantly higher in rhizosphere than in non-rhizosphere soil. On the contrary, NH4+-N and total N, PDA, the abundance of AOB, and nirK and nirS genes were significantly higher in non-rhizosphere soil. The results indicated that the N transformations in rhizosphere and non-rhizosphere soils were differently affected by soil application of Mo fertilizer, and rhizosphere played a more important role in soil N cycle processes. The regulatory effects of Mo on these processes were to increase plant biomass and N uptake, promote the NO3--N accumulation in rhizosphere soil, and weaken the denitrification in both rhizosphere and non-rhizosphere soils.
Keywords: Molybdenum; Nitrogen transformation; Non-rhizosphere; Rhizosphere; Soil.